Electrical system



April 11, 1967 Filed Aug. 30, 1963 M. I ROSENBERG ET AL ELECTRICAL SYSTEM 4 SheetsSheet 1 FIGI. /0 2 /6 LOAD c -----I--- EN INE *ALTERNATOR APPARATUS F "'"l ALTERNATOR 38 l 36 FIELD l A I SIRS-In a SENS'NG ADJUSTING '|T- CIRCUIT curr i 25 34 40 I *I sI-IORT TEMPERATURE I HELD CIRCUIT COMPENSATION l FORCING "RRoTEcTION l cIRcuIT |RU|T cIRcuIT I 4 k v Fl 46 FIELD FORCING FIELD ANTI MAGNET'C cIRcuIT sATuRATION HUNT U ICOMPENSATION cIRcuIT cIRcuIT L I I FIGZ.

ENOINE fi l ExcITER ALTERNATO T 22 1 T ExcITER ALTERNATOR FIELD FIELD REGULATOR INVENTORSI MERTON I. ROSENBERG BY WALTER c. BOI-IAKE WM 6610M ATTYS.

April 11, 1967 RQSENBERG ET AL 3,314,000 I ELECTRICAL SYSTEM 4 Sheets-Sheet 2 Filed Aug 30, 1963 W Twa ma Nam PM 35min? Q oJ INVENTORSZ MERTON l. ROSENBERG WALTER G. BOHAKER W; fiQw/W ATTYS' M. l. ROSENBERG ETAL 3,314,000

April 11, 1967 ELECTRICAL SYSTEM 4 Sheets- Filed Aug. 30

Sheet 5 FIGS.

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C D A O L L L U F INPUT TO BRIDGE (v0 LTS) CONTROL VOLTS FIG. 6..

ruu. WAVE RECTIFICATION FULL LOAD PART LOAD C {I {I LIGHT LOAD FIG.8..

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WITH FIELD FORCING SATURATION AMPLIFIER OUII'PUT AMPLIFIER OUTPUT FIELD CURRENT VOLTAGE VOLTAGE mvcwrons; ROSENBERG MERTON I. By WALTER G. BOHAKER ATTYS.

April 11, 1967 M. l. ROSENBERG L 3,314,000

ELECTRICAL SYSTEM Filed Aug. 30, 1965 4 Sheets-Sheet 4 F IG. IOA

F l I05.

F|G. IOC.

INVENTORSZ MERTON ROSENBERG B WALTER G.

v BOHAKER W W ATTYS.

United States Patent 3,314,000 ELECTRICAL SYSTEM Merton I. Rosenberg and Walter G. Bohaker, Springfield,

Mass., assignors to American Bosch Arma Corporation, Garden Cit N.Y., a corporation of New York Filed Aug. 30, 1963, Ser. No. 305,596 4 Claims. (Cl. 322-45) This invention relates to systems for controlling the output of a source of electrical power having a control element, by applying to said control element a control signal derived from the output of said source. More particularly it relates to voltage regulators for stabilizing or otherwise controlling automatically the output voltage of a generator :of electrical voltage, where the term generator is used broadly to include an alternator, for example.

Systems are known in the prior art which are intended to stabilize the output voltage of an electrical generatorat a predetermined rated voltage despite tendencies for it to change in response to such factors as changes in load drawn from the generator, changes in speed of the power source driving the generator, changes in ambient temperature, and others. This has been accomplished in the past to a substantial degree by sensing output voltage and/or current of the generator to derive control signals and feeding back the control signals to control the current through the field element of the generator in degenerative phase, thereby to oppose deviations from the desired output voltage. In such systems it is desirable that deviation of the generator output voltage from the desired rated voltage be held to as small a value as possible, desired output voltage be regained as soon as possible. It is also desirable in certain applications that the stabilization the effective over a wide range despite tendencies for the field element to become saturated for high currents through it, and that the generator system be adapted to start up quickly without need for an external current supply. In addition in some instances it is desirable that, when the generator output is short-circuited, the generator be made to deliver a high current output for a period sufiicient to operate a high-level circuit breaker, so that the generator can be used safely even with load apparatus using a circuit breaker which operates only at such relatively high levels.

It is therefore an object of the invention to provide a new and improved voltage regulating system of the class in which signals derived from the output of the system are fed back to a control element of .a voltage-generating source.

' Another object is to provide such a system which maintains the output voltage of said generator very close to a predetermined rated voltage level.

A further object is to provide such a system which is capable of providing rapid generator voltage build-up on starting without requiring an additional current source.

Another object is to provide such a system which is effective to provide stabilization of said output voltage over a wide range of variation in factors tending to change said output voltage, despite the fact that the control element used to control automatically said output voltage exhibits a saturation effect at relatively low values of the control signal applied thereto.

It is also an object to provide such a system in which compensation is provided to stabilize the output voltage of the source against changes in temperature.

A further object is to provide such a system in which, upon substantial short-circui-ting of said source, a large pulse of current is produced and maintained for a time sufficient to actuate a high-level circuit breaker.

Another object is to provide a new and improved and that if a substantial deviation does occur the ICC .for producing a control voltage varying in dependence on the magnitude of the output voltage of the source to be regulated, which control voltage is fed back in effect to a control element of the source, such as the field element of a generator, to control the output voltage. The voltage sensing circuit is such that the control voltage is of one polarity for the relatively small output voltages produced when the source is first started up and is fed back to the control element in regenerative phase to assist in rapid build-up of the source output voltage; however,

when the output voltage has built-up to a predetermined extent the control voltage changes to the opposite polarity and increases in said opposite polarity for further increases in output voltage. Accordingly the feedback control is then in degenerative phase so as to oppose further increases in output voltage and to stabilize it at a predetermined level during normal operation. This voltagesensing circuit is constructed and adjusted so that during normal operation the control voltage produced thereby is of said opposite polarity Preferably a load-current sensing circuit is also used which senses the magnitude of the load current drawn from the source and produces a control voltage for effectively increasing the gain of the feedback circuit for higher load currents, thereby providing closed stabilization or regulation at high loads without introducing system instability for smaller loads. Preferably also, the control voltages from the voltage-sensing and load-current sensing circuits are fed back by way of an amplifier, and a negative temperature coeflicient element is disposed between the load-current sensing circuit and the amplifier to compensate for fall-off of source output voltage with increased temperature.

According to another feature, the hunting which tends to occur in the source output voltage, as well as in the control voltage supplied from the amplifier to the control element, due to the feedback-control action of the regulating system, is minimized while retaining the ability of the system to provide rapid correction and to recover quickly following sudden extreme load changes, such as sudden change from full load to no load, by means of a novel anti-hunt circuit. This anti-hunt circuit employs capacitive means sufiiciently large to feed back hunting variations from the output of the amplifier to its input, while blocking direct voltages, and voltagebreakdown means such as a Zener diode connected in circuit with the capacitive means to limit the voltage level to which the capacitive means can charge in response to decreases in load, thereby preventing the slow recovery times which would otherwise be produced by full charging and subsequent discharging of the capacitive means.

According to another feature a wide range of control for the regulating system is provided despite a relatively low saturation level of the control element of the source above which the control capability of the control element is greatly decreased; this is accomplished by means of one or more circuits having non-linear voltage-current characteristics disposed in the regulating system so that when the control voltage applied to the control element increases from below to above the level for which substantial saturation of the control element begins, the non-linear circuit provides a more rapid increase in saidcontrol voltage to counteract the saturation effect.

A further feature involves a novel short-circuit protection circuit arrangement for providing and maintaining for a substantial interval a large output current from the source when the output terminals of the source are shortcircuited, even though the regulator system includes an element such as a magnetic amplifier supplied with operating voltage from the output terminals of the source and which therefore tends to reduce the source output when the above-mentioned short-circuiting occurs. The pre ferred form of the latter circuit is used with a source which provides an additional current in different phase from that normally used to operate the magnetic amplifier, and uses the latter additional current to increase greatly the output of the magnetic amplifier when a short-circuit occurs, in a manner described in detail hereinafter. In this manner the source is enabled to provide adequatelyhigh current for a sufficient time to operate a high-level circuit breaker upon the occurrence of a short-circuit in the load apparatus.

These and other objects and features of the invention will be more readily appreciated from a consideration of the following detailed description of a particular embodiment thereof, taking together with the accompanying drawings in which:

FIGURE 1 is a block diagram illustrating the functional interrelationships of various elements of a preferred embodiment of the invention;

FIGURE 2 is a block diagram illustrating an alternative overall arrangement of a system employing the inven tion;

FIGURE 3 is a schematic circuit diagram representing in detail a preferred embodiment of the invention;

FIGURES 4 through 9 are graphical representations illustrating certain characteristics of particular elements of a preferred embodiment of the invention; and

' FIGURES 10A, 10B, and 10C are schematicdiagrams illustrating the regulator connections for various phase arrangements of the alternators.

' Referring'first to FIGURE 1, the block diagram therein indicates the broad functional elements and their interrelationships in accordance with the invention as applied to a voltage source comprising a simple form of electrical generator without separate exciter. As shown, an engine 10, provides mechanical drive for alternator 12, which has the usual alternator field 14 and which supplies output power to any suitable load apparatus 16, which may include a circuit breaker. The regulator 18 is supplied with output power from the alternator and applies a controlled current to the alternator field 14 to maintain constant the voltage supplied to the load apparatus 16. Accordingly the alternator field serves as a control element for the vgenerator. It will be understood that other types of generators having other types of control elements may be utilized, for example as shown in FIGURE 2 Where the engine 10 drives the alternator 19 and exciter 20 of an exciter-type generator, the exciter controlling the alternator field 21 and the regulator 18 being connected between the output of the alternator and the exciter field 22.

As shown in FIGURE 1, regulator 18 includes a magnetic amplifier circuit 26 the output of which is passed through field-forcing circuit 28 to the alternator field 14 to control the strength of magnetic field in the generator and hence the generator output. The magnetic amplifier circuit 26 is supplied with gating signals from the output of alternator 12 by way of a connection which includes short-circuit protection circuit 34, the function of which is to produce sufficient output from the amplifier circuit to force the alternator field 14 so that the alternator 12 sustains a short circuit current for a sufiiciently long time to trip a relatively high current circuit breaker in the load apparatus 16 upon the occurrence of a short circuit or extremely heavy load produced by the load apparatus.

Magnetic amplifier circuit 26 is provided with four input control signals which act automatically to control the magnitude of the output of the amplifier circuit to the alternator field 14. One of these controls is derived from the output of the alternator 12 by way of voltage sensing and adjusting circuit 36, and acts in a direction to counter increases or decreases in the output voltage of the alternator during normal operation, while providing regenerative feedback during initial voltage build-up when the alternator is first started.

Another control signal is derived by the load sensing circuit 38, which senses the alternator output current and supplies a control signal to the magnetic amplifier by way of temperature compensation circuit 40 and field forcing circuit 42. The direction of control is in a direction to increase the alternator field current, and hence the alternator output voltage, as the alternator load current increases. The temperature compensation circuit 40 responds to ambient temperature changes which tend to change the alternator output voltage, to cause the magnetic amplifier to produce compensating changes in the current through the alternator field 14. The function of the fieldforcing circuits 28 and 42 is to compensate for saturation of the magnetic element of the alternator field 14 in re: sponse to high field currents, by producing a greater rate of increase of alternator field current in response to control voltage for such high field currents than for alternator field currents below the saturation level.

Although not essential, preferably another control for magnetic amplifier circuit 26 is derived from the output of the magnetic amplifier by way of field saturation compensation circuit 44. This circuit arrangement serves also to compensate for the non-linear characteristics of the alternator field produced by magnetic saturation therein, and may include a cont-r01 for trimming the amount of feedback provided by the regulator.

The remaining control for magnetic amplifier circuit circuit 46, the phase of the feedback in this case being negative. The function of the anti-hunt circuit 46 is to minimize those variations in the output voltage of alternator 12 which the regulator itself tends to introduce, while at the same time permitting the regulator to respond with adequate speed in compensating for load voltage or load current variations and in recovering from the effects of such variations.

With this general organization of the system in mind, the detailed circuitry of a specific embodiment of the invention suitable for one application thereof will now be described in detail.

Referring now to FIGURE 3, theinvention as shown is applied to a single-phase delta-connected A.C. alternator of a type involving noexciter, and employing an alternator field 50 having a pair of current input terminals 52 and 54, connected in series with a field winding 56 disposed in conventional manner about a suitable mag- V netic material, and a multi-phase winding arrangement 60 coupled thereto and including three windings 62, 64 and 65 arranged to supply output power to load apparatus 16 by way of leads 66 and 68. Terminals 70 and 72 are provided between the adjacent ends of windings 62 and 65, while terminals 74 and 76 are provided between the adjacent ends of windings 64 and 65, the current paths between the members of each pair of terminals being provided by connections within the regulator 18 as described hereinafter.

The magnetic amplifier circuit 26 for regulator 18 in this case comprises a Ramey-type magnetic amplifier of the full-wave type, using two magnetic cores 80 and 82 of square-loop material such as 50% nickel and 50% iron,'and'two respective gate-windings 84 and "86. Each of the cores '80 and 82 has associated with it four con with that of resistors 138 and 141,

ably being counter-wound so that undesirable effects of electromotive force of self-induction are minimized.

The gating signals for the magnetic. amplifier are supplied from across the output leads 66 and 68 of the genly interconnected, While diodes 114 and 116 have their anode elements directly interconnected. The arrangement is such as to produce between the interconnection 118 of diodes 110 and 112, and the interconnection 120 of diodes 114 and 116, a unidirectional pulsating output voltage from the amplifier having an average value which depends upon the control current flowing through the control windings 90, 92, 94, 96, 98, 160, 102 and 104, according to known principles of magnetic amplifier operation.

The voltage generated between interconnections 118 and 120 is supplied by way of field-forcing circuit 28 to the input terminals 54 and 52 respectively, of the alternator field 5t). Increases in the voltage between interconnections 118 and 12 0 therefore produce increases in the field current and greater output from the generator across output leads 66 and 63. vAccordingly, the voltage produced by the generator depends upon, and is controlled by, the current through the above-mentioned control windings of the magnetic amplifier 26.

The voltage-sensing and adjusting circuit 36 has its input terminals connected between output leads 66 and 68 of the generator and has its output leads 121 and 122 connected in series with control windings 94 and 96 of amplifier 26. It is the function of circuit 36, broadly, to respond to increases in magnitude of the voltages between output leads 66 and 68 of the generator to increase the current control windings 94 and 96 in the positive-feedback sense while the generator output voltage is initially building up, and therefore to produce an increased output voltage at interconnections 118 and 120 and an enhanced field current [for assisting in this building up; and, after stable operating conditions have been produced, to respond to any changes in generator output voltage to change the current through control windings 94 and 96 in the negative-feedback sense, thereby to oppose 'thelastmentioned changes in generator output voltage.

To this end the output voltage at leads 66 and 68 is supplied by way. of fixed. current-limiting resistor 130 and variable series resistor 132 to opposite points on a conventional bridge rectifier circuit 134, the other diametriq cally-opposed terminals of which bridge rectifier circuit are interconnected by the resistor'and Zener-diode bridge circuit 136. The latter circuit consists of a first series combination of a resistor 138 and Zener diode 140, and, in parallel with it, a second series combination of another resistor 141 and a second Zener diode 142. The order of the resistors and Zener diodes in the two branches of the circuit is opposite, and both diodes are poled so that their cathodes are connected to the more positive end of circuit 136. Output from circuit 136 is taken between the two center taps 144 and 146 in the two parallel branches thereof.

In operation, when the voltage between generator output terminals 66 and 68 is very low, as when the generator is started with only a small remanent'flux existing in .the alternator field, the voltage across the Zener diodes 140 and 142 is relatively low and they are therefore in their low-current, reverse-biased condition, presenting a high resistance to current flow. The impedance of the Zener diodes is therefore at these times large compared so that the voltage at center tap 144 is more positive than that at center tap 146, producing a current through control'windings 94 and 96 in the polarity to increase the current in the field winding 56 and rapidly increase the output voltage of the generator in regenerative fashion.

Referring to FIGURE 4, which is a plot showing as ordinates the average voltage of interconnection 144 relative to that of interconnection 146, and showing as abscissae the average voltage applied across Zener diode bridge circuit 136 by rectifier bridge 134, the operation for low generator output voltages is represented by the initial portion of the curve as it increases toward a maximum value of average output voltage. However, with increased input voltage to circuit 136 the Zener diodes begin to become conductive during the more positive portions of the input half-waves, with the result that a negative component of output voltage is thereby introduced to oppose the positive component. The average output voltage at interconnection 144 with respect to interconnection 146 therefore increases less rapidly with input voltage, and then begins to fall. For still larger generator output voltages the average output voltage of bridge 136 becomes zero and then becomes negative with respect to the voltage at interconnection 146. When the voltage at tap 144 has a reference negative value such as A in FIGURE 4, corresponding to the occurrence of the rated output voltage of the generator, .the feedback for the system is degenerative, rather than regenerative, in that if an increase in generator output voltage due, for example, to decrease in load should occur, the average voltage at interconnection 144 will increase in a negative sense toward a point such as B in FIGURE 4, which produces an increase in the negative current through the control windings 94 and 96 so as to decrease the current through field winding 56 and oppose the above-mentioned generator output voltage increase. Similarly, a decrease in generator output voltage, due for example to an increase in load, will produce a shift toward point C of FIGURE 4 and a corresponding increase in field current so as to produce an opposing increase in generator output voltage.

FIG. 5 illustrates the relationship between the average control voltage across control coils such as 94 and 96 of magnetic amplifier 26, and the average current produced at the output of the magnetic amplifier. The operating points A, B, and C of FIGURE 5 correspond to the similarly labelled points of FIGURE 4. Thus, as shown in FIGURE 5, the negative control voltage from bridge circuit 136 operates the magnetic amplifier near the center of its operating range. at point A when normal output voltage for the generator has once been established, although the magnetic amplifier output is shifted toward the lower-current point B when the generator output voltage tends to increase and toward the higher-current point C when it tends to decrease.

The instantaneous magnetic amplifier outputs producing the average conditions shown in FIGURE 5 are represented in FIGURE 6, in which the parts A, B and C thereof are graphs-having time as a common abscissae and having as ordinates the instantaneous voltage produced at the output terminals 118 and of the magnetic amplifier 26 for dilferent values of control voltage applied thereto. Graph 6A corresponds to the normal operation of the generator at the rated-voltage points indicated by the corresponding points A in FIGURES 4 and 5. Graph 6B represents this output voltage when, due to decreased load or for other reasons, the output voltage of the generator tends to increase. Graph 6C shows the magnetic amplifier output voltage when the generator voltage tends to fall, corresponding to points C in FIGURES 4 and 5. Y

The normal operating output voltage, or rated voltage, of the generator is adjusted to point A on the negative portion of the characteristic of FIGURE 4 by varying the position of the tap on variable resistor 132. The resistor I 150 and the inductor 152 in series with control windings 94 and 96, and capacitor 154 in shunt therewith, provide voltage bridge circuit 136, while at the same time providing a time constant sufficiently short to enable adequate control in response to rapid changes in generator output voltage. In addition, the latter filter circuit helps to prevent application to voltage bridge cricuit 136 of any'unbalanced signals induced in the control windings 94 and 96 by the gating signals in the magnetic amplifier 26.

As mentioned previously, there is preferably connected in series with field winding 56 a field-forcing circuit 28, comprising the parallel combination of resistor 160 and Zener diode 162, the Zener diode 162 being connected in the polarity such that its cathode is connected directly to the positive output terminal 118 of magnetic amplifier 26 and hence is reverse biased. The value of resistor 160 is selected so that, when current less than that required to produce saturation of the magnetic material of the alternator field 50 is passing, the voltage across resistor 160 is insufficient to produce substantial reverse current through Zener diode 162. However, when the current to the field coil increases to the level at which substantial saturation of the magnetic material of the field begins to occur, the voltage across resistor 160 becomes sufficiently large to produce reverse breakdown of the Zener diode 162, so that the current through the field coil increases more rapidly than previously with increases in the output voltage of the magnetic amplifier 26. The result is that the magnetic field produced by coil 56 is forced to increase substantially despite saturation of the magnetic material, and the range of control of the field current of the generator output voltage is thereby substantially extended.

More particularly, FIGURE 7 shows the general nature of the relationship between the current through field coil 56 plotted as abscissae and the magnetic flux produced by the alternator field plotted as ordinates, illustrating that for an initial range of low field currents the magnetic flux increases relatively rapidly and substantially linearly with field current, until at a point D saturation begins to occur,,as indicated by the substantially less rapid increase of magnetic flux with field current. Accordingly, past the saturation point D the magnetic amplifier 36 would be required to provide much larger increases in current in order to produce a given increase in magnetic flux for controlling the generator output.

FIGURE 8 shows the elfect of the Zener diode characteristic which compensates for this saturation effect. In FIGURE 8, absicissae represent the output voltage of magnetic amplifier 26 while ordinates represent the corresponding field current. As shown, in a relatively low range of amplifier output voltages below the point E the field current increases substantially linearly and at a relatively low rate, but after point E is reached the field current increases at a substantially higher rate because of conduction through Zener diode 162. The field current at point B at which the Zener begins to conduct at a higher rate is made substantially the same as the field current corresponding to point D in FIGURE 7 at which saturation of the alternator field becomes substantial, by approprate selection of the value of resistor 160 and the breakdown voltage of the Zener diode 162. The result is the relationship, illustrated by the graph of FIGURE 9, between magnetic amplifier output voltage plotted as abscissae and alternator output voltage produced in response thereto plotted as ordinates, wherein point F corresponds to the above-mentioned point D of FIGURE 7. In FIGURE 9 it is shown that the exciter field voltage increases at a relatively rapid rate in response to increases in output voltage of amplifier 26 even substantially beyond the knee of the saturation curve of the alternator field, establishing an additional range of control due to the phenomenon described hereinbefore and designated herein as field forcing. Summarizing then the operation of the portion of the system thus far described in detail, when the generator is first started up the small amount of remanent magnetism of the magnetic core of the alternator field provides some generator output voltage which is rectified and provided in regenerative phase by way of magnetic amplifier 26 and field forcing circuit 28 to the alternator field to increase the current and magnetization therein, which in turn increases the generator-output voltage,'resulting in a rapid regenerative build-up of generator output voltage, until the Zener diodes 140 and 142 cause the feedback control voltage to drop to zero-and then to reverse in polarity so as to establish a negative feedback control for normal full voltage operation. Accordingly, no external current source, such as a battery, is required to build up magnetization of the alternator field when the generator is started up.

Additional control for magnetic amplifier 26 is provided by the load sensing circuit 38. The input to this circuit comprises the transformer primary winding 200 of transformer 201 connected in series between terminals 70 and 72 of alternator armature 60, thereby to sense the magnitude of the load current drawn from the generator by load apparatus 16. The secondary winding 202 of transformer 201 is connected at one end to a resistor 204 and thence to one input terminal 205 of bridge rectifier 206. Secondary 202' is also provided with a variable resistor 208 connected between its other end and a terminal 210, and with two additional variable resistors 212 and 214 connected between respectively different intermediate taps on a secondary 202 and terminals 216 r and 218 respectively. A variable connection 220 is provided which may be connected at will to any of the terminals 210, 216, and 218, and in the case shown is connected to terminal 216. The other terminals are connected to tap 220 when the regulator is connected to alternators having other types of .winding arrangements, as described hereinafter.

Variable tap 220 is connected to a terminal 222 of bridge 206 diametrically opposite terminal 205 thereof, so as to apply across the input to bridge 206 a voltage varying substantially in proportion to the load current of the generator output. Bridge 206 is of conventional bridge-rectifier form and may utilize, for example, silicon diodes for each of the four diode elements thereof, which may be connected similarly to the diodes in bridge circuit 134.

The output terminals 224 and 226 of the bridge circuit 206 are connected to the series combination of control windings 90 and 92 of magnetic amplifier 26, terminal 224 being connected thereto by way of temperature compensation circuit 40 and field-forcing circuit 42. The polarities of the direct voltages produced, and of the control windings 90 and 92, are such that an increase in load on the generator, which normally tends to decrease the voltage supplied to the load apparatus 16, produces an increase in the current through control windings 90 and.

92 so as to increase the output voltage of the magnetic amplifier by regenerative feedback and increase the current through field coil 56. In effect the circuit operates to increase the gain of the regulator at higher load currents for which higher gain does not produce instability as it would at lower load currents, thereby improving the closeness of regulation at high load currents. Furthermore, the use of such a load-sensing feedback circuit in addition to the voltage sensing control circuit described previously provides for quicker control of the output voltage.

The temperature compensation circuit 40 is located, as 9 shown in FIGURE 3, in series with the lead supplying current from the load sensing circuit to the control windings 90 and 92, and comprises a thermistor 230 having a negative temperature coefiicient of resistance, shunted by a variable resistor 232. This circuit is designed to compensate for the decrease in output voltage of the generator which tends to occur when the ambient temperature increases. In operation, when the ambient temperature increases, tending to produce a decrease in generator output voltage, the resistance of thermistor 230 also de- 9 creases, increasing the control current to control windings 90 and 92 so as to oppose the decrease in generator output voltage. By suitable adjustment of the value of variable resistor 232 a high degree of temperature compensation over a relatively wide range can readily be obtained.

The field-forcing circuit 42, also located in series between the load sensing circuit and control windings 90 and 92, comprises Zener diode 234 and variable resistor 236 in parallel therewith. The latter circuit functions similarly to field-forcing circuit 28 in that when the current passing through resistor 236 to control windings 90 and 92 increases beyond a predetermined point for which saturation of alternator field 50 begins, the voltage then produced across variable resistor is sufiicient to cause substantial reverse conduction in Zener diode 234, thereby increasing more rapidly the current supplied to control coils 90 and 92 of the magnetic amplifier 26 when needed to compensate for alternator field saturation and also for induction motor starting as described previously herein. Variable resistor 236 will normally be adjusted to provide inception of Zener diode conduction at the desired current level, and can be varied in connection with variable resistor 232 to achieve temperature compensation over the desired temperature range.

Accordingly, the feedback circuit last described combines a load-sensing control, temperature compensation control, and an additional field-forcing function within a common feedback circuit loop using a common pair of control windings of the magnetic amplifier.

An additonal feature of the invention is the short-circuit protection circuit 34, which in this example comprises an iron-core transformer 260 having its primary 262 connected in series between terminals 74 and 76 of the alternator arrangment 60, and having its secondary 264 connected in parallel with a resistor 266, the latter parallel combination being in series between output lead 68 of the generator and the interconnection of the two gating coils 84 and 86 of magnetic amplifier 26. The transformer preferably provides a 180 phase shift from primary to secondary, and in the present example the phase of current in winding 64 is 120 out of phase with that in winding 65, so that the voltage induced in the secondary 264 by the primary 262 during normal operationis only 60 out of phase with that produced in the secondary by alternator winding 65. In addition, the transformer winding arrangement is preferably such that normally the magnitude of voltage induced in thetransformer secondary by the primary'is small. compared with that due to winding 65. Accordingly, during normal operation the current in primary 262 has only a relatively minor effect on the gating signal to the magnetic amplifier. However, when a short-circuit occurs in the load apparatus 16 the voltage across output conductors 66 and 68 of the alternator approaches zero, while the highcurrent produced through alternator winding 64 by the short-circuiting induces a high voltage in secondary 264 which is applied to the gating windings of the magnetic amplifier and thence to the field element of the alternator to increase greatly the output current of the generator, typically to four or five times the normal full load current for several seconds. Accordingly enough electrical current is delivered to the load apparatus to operate even a highcurrent circuit breaker therein, which otherwise might not be operated.

In the particular form of the invention shown, a field compensation circuit 44 is connected between the output terminals of the magnetic amplifier 26 and control windings 102 and 104 thereof. Input to the field compensation circuit is applied across the resistor 300 and the resistance of potentiometer 302 connected in series. The voltage developed between the adjustable tap of potentiometer 302 and the opposite end of resistor 300 is applied to a filter circuit comprising series inductor 304 and shunt capacitor 306 by way of an isolating and current-limiting resistor 308 so that the voltage developed across capacitor 306 is a smoothed D.C.-voltage varying substantially in proportion to the avenage output voltage of magnetic amplifier 26. The latter smoothed voltage is fed back to the control windings 102 and 104 by way of the field-forcing circuit comprising the parallel combination of resistor 310 and Zener diode 312, and by way of the series current-limiting resistor 314. The feedback to the input control windings is in regenerative phase. Accordingly, when the input to any of the control windings of the magnetic amplifier increases to the point where the current to the alternator field 50 is in the range for which field saturation begins to occur, the voltage fed back by the field compensation circuit further augments the output of the magnetic amplifier to produce a more than linear increase in field current, thereby compensating further for the less-than-linear increase in magnetic flux due to the core saturation in the alternator field. Potentiometer 302 provides for adjustment of the amount of positive feedback occurring, and the series limiting resistors reduce the loading effect of the circuit on the output of the magnetic amplifier and limit the current fed back to the control windings 102 and 104, the values of the circuit elements being such as to prevent runaway or instability in the magnetic amplifier.

A further feature of the invention comprises the antihunt circuit 46 also connected between the output terminals of the magnetic amplifier 26 and the input thereof, in this case to control windings 98 and 100. In normal operation, the generator output voltage tends to oscillate from above to below its desired value due to the feedback control action of the regulator. Such undesired oscillation or hunting is opposed by the antihunt circuit 46, which also improves voltage stability at no load. The input to this circuit is applied from the output connections 118 and 120 of the magnetic amplifier, and is supplied to control windings 98 and in series by way of series resistor 400, capacitor 402 and inductor 404. Resistor 406 and the series combination of Zener diode 408 and ordinary diode 410 are connected respectively between connection and opposite sides of capacitor 402 as shown.

In operation of the anti-hunt circuit, the capacitor 402 permits feedback in degenerative phase, by way of resistor 400 and inductor 404, of variations of the magnetic amplifier output due to hunting, while blocking direct voltages. In order to provide appropriate feedback under normal operating conditions the capacitor will normally be relatively large. However this introduces the difliculty that if a heavy load is applied and then removed abruptly, the capacitor will charge up rapidly to a high value but will require appreciable time to discharge thereafter, and hence will not respond as quickly as is desired. Zener diode 408 remedies this condition by breaking down when the voltage on capacitor 402 tends to rise above a predetermined value, thus providing a low-resistance shunt path for current by way of diode 410 which arrests further charging of the capacitor. Accordingly the capacitor discharges to a given voltage more rapidly than otherwise to provide the desired rapid recovery. vDiode 410 is poled to permit easy current flow when Zener diode 408 breaks down, and to block flow in the opposite direction to prevent short-circuiting of opposite polarity signals by the Zener diode.

FIGURES 10A, 10B and 10C indicate the manner in which the regulator may be connected to generators of the three-phase delta, three-phase Y and single-ph-ase open V. types, respectively. The terminals and leads indicated by number and letter combinations in each case are to be connected to the regulator in the same manner as the correspondingly-numbered terminals and leads in FIG- URE 3. When a generator of the single-phase open V type is used, connection 220 of FIGURE 3 is moved to contact terminal 218, and when the generator is of the three-phase delta or three-phase Y type this connection is moved to terminal 210.

Accordingly there is provided a regulator which, while requiring no moving parts, provides very close regulation of generator output voltage, for example to within a few hundredths of a percent, despite substantial changes in speed of the engine driving the generator, in the load current drawn from the generator, in ambient temperature, in characteristics of the generator, and in characteristics of circuit elements of the regulator, even though various of these changes may occur rapidly. At the same time actuation of protective fusing is assured on shortcircuiting of the generator, and rapid build-up of generator voltage on starting-up is provided Without need for an external current source. The regulator is stable and reliable in operation, making it practical for it to be hermetically sealed, and operates effectively even with a generator which is less than ideal in that its field saturates at relatively low field current. It will be understood that while use of all of the various features of the invention in combination provides the best results in most applications, less than all may be used to advantage in applications in which one or more of the features provided are not considered necessary.

While the invention has been described with particular reference to specific embodiments thereof, it may be embodied in a variety of forms differing from those specifically described herein without departing from the spirit and scope or the invention as defined by the appended claims.

' We claim:

1. In a voltage regulator system of the class adapted to provide stabilization of an electrical generator having a current-controlled magnetic field element by feeding back a portion of the output voltage of said generator in degenerative phase to control the current through said field element, said generator being responsive to increases in current in said field element to increase said output voltage at a relatively rapid rate for values of said current in a first relatively low range and to increase said output voltage at a substantially lower rate for values of said current in a second, higher range for which substantial saturation of said field element occurs:

means for deriving from said output voltage a control voltage varying in accordance with variation in the magnitude of said output voltage;

means for feeding back said control voltage to said field element to vary the current in said field element in the sense to oppose changes in said output voltage; and

means for'providing a more rapid increase in said control voltage with changes in said output voltage for values of said control voltage producing values of :said field current in said second range than for values of said control voltage producing values of said field current in said first range;

said last-named means comprising the parallel combination of a zener diode and a resistive element disposed in said means for feeding back said control voltage, said zener diode being .poled to break down in its reverse-conduction direction when the voltage across said resistive element exceeds a predetermined voltage, said resistive element being responsive to current therethrough to produce a voltage across itself which is below said predetermined voltage for values of said field current in said first range and above said predetermined voltage for values of said field current in said second range.

2. In a voltage-stabilized electrical generator system:

an electrical generator having output terminals and output windings for producing output voltages at said output terminals for application to load apparatus susceptible to short-circuiting, and having a field element responsive to increases in current therein to increase said output voltage; i

a voltage regulator having input terminals supplied With said output voltage and having output terminals connected to control said current in said field element normally to oppose departures of said output voltage from a predetermined value thereof;

said regulator comprising a magnetic amplifier having gating windings which are normally supplied with operating voltage from said output terminals of said generator and which are connected to said field element to provide said control of current therein;

means responsive to increases in current drawn from said generator by said load apparatus upon shortcircuiting therein to generate and supply to said gating windings a voltage suflicient to increase sharply said current in said field element, threby to maintain a high current from said generator for a time sufficient to operate a high-current circuit-breaking device connected thereto;

said last-named means comprising a transformer having a primary winding and a secondary Winding, said gating windings being connected to said output terminals of said generator by way of said secondary winding, said generator comprising a plurality of mult-phase output windings, one of which output windings is connected across said output terminals of said generator and another of Which output windings is connected in series with said primary winding of said transformer; and

field-forcing means connected between said output terminals of said regulator and said field element, said field-forcing means comprising the parallel combination of a voltage-breakdown device and a currentconductive element, said voltage-breakdown device being normally non-conductive for relatively smaller output voltages at said regulator output terminals but strongly conductive for relatively larger output voltages at said regulator output terminals.

3. Apparatus in accordance with claim 1, in which said means for deriving from said output voltage .a control voltage includes a magnetic amplifier responsive to said output voltage to produce said control voltage and having output terminals and input control terminals, said means for providing a more rapid increase in said control voltage being connected between said output terminals of said magnetic amplifier and said field element.

4. Apparatus: in accordance with claim 3, comprising additional feedback means for feeding back a portion of the output signal at said output terminals of said magnetic amplifier to said input control terminals in regenerative phase, said additional feedback means including a parallel combination of an additional zener diode and an additional resistive element in shunt with said zener diode, said last-named parallel combination being disposed in series between said output terminals of said magnetic amplifier and said input control terminals thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,709,776 5/ 1955 Evans et al 32281 X 2,768,344 10/ 1956 McKenna. 2,996,654 8/1961 Livingston 32219 X 3,027,509 3/1962 Lamaster 32225 3,045,171 7/1962 Heins et al 32225 MILTON O. HIRSHFIELD, Primary Examiner. J. J. SWARTZ, Assistant Examiner. 

1. IN A VOLTAGE REGULATOR SYSTEM OF THE CLASS ADAPTED TO PROVIDE STABILIZATION OF AN ELECTRICAL GENERATOR HAVING A CURRENT-CONTROLLED MAGNETIC FIELD ELEMENT BY FEEDING BACK A PORTION OF THE OUTPUT VOLTAGE OF SAID GENERATOR IN DEGENERATIVE PHASE TO CONTROL THE CURRENT THROUGH SAID FIELD ELEMENT, SAID GENERATOR RESPONSIVE TO INCREASES IN CURRENT IN SAID FIELD ELEMENT TO INCREASE SAID OUTPUT VOLTAGE AT A RELATIVELY RAPID RATE FOR VALUES OF SAID CURRENT IN A FIRST RELATIVELY LOW RANGE AND TO INCREASE SAID OUTPUT VOLTAGE AT A SUBSTANTIALLY LOWER RATE FOR VALUES OF SAID CURRENT IN A SECOND, HIGHER RANGE FOR WHICH SUBSTANTIAL SATURATION OF SAID FIELD ELEMENT OCCURS: MEANS FOR DERIVING FROM SAID OUTPUT VOLTAGE A CONTROL VOLTAGE VARYING IN ACCORDANCE WITH VARIATION IN THE MAGNITUDE OF SAID OUTPUT VOLTAGE; MEANS FOR FEEDING BACK SAID CONTROL VOLTAGE TO SAID FIELD ELEMENT TO VARY THE CURRENT IN SAID FIELD ELEMENT IN THE SENSE TO OPPOSE CHANGES IN SAID OUTPUT VOLTAGE; AND MEANS FOR PROVIDING A MORE RAPID INCREASE IN SAID CONTROL VOLTAGE WITH CHANGES IN SAID OUTPUT VOLTAGE FOR VALUES OF SAID CONTROL VOLTAGE PRODUCING VALUES OF SAID FIELD CURRENT IN SAID SECOND RANGE THAN FOR VALUES OF SAID CONTROL VOLTAGE PRODUCING VALUES OF SAID FIELD CURRENT IN SAID FIRST RANGE; SAID LAST-NAMED MEANS COMPRISING THE PARALLEL COMBINATION OF A ZENER DIODE AND A RESISTIVE ELEMENT DISPOSED IN SAID MEANS FOR FEEDING BACK SAID CONTROL VOLTAGE, SAID ZENER DIODE BEING POLED TO BREAK DOWN IN ITS REVERSE-CONDUCTION DIRECTION WHEN THE VOLTAGE ACROSS SAID RESISTIVE ELEMENT EXCEEDS A PREDETERMINED VOLTAGE, SAID RESISTIVE ELEMENT BEING RESPONSIVE TO CURRENT THERETHROUGH TO PRODUCE A VOLTAGE ACROSS ITSELF WHICH IS BELOW SAID PREDETERMINED VOLTAGE FOR VALUES OF SAID FIELD CURRENT IN SAID FIRST RANGE AND ABOVE SAID PREDETERMINED VOLTAGE FOR VALUES OF SAID FIELD CURRENT IN SAID SECOND RANGE. 